Temperature influence on potato leaf and branch distribution and on canopy photosynthetic rate

Mature potato (Solanum tuberosum L. cv. Kennebec) canopies are composed of leaves originating from main- and axillary-stem branches. Canopy leaf distribution and its corresponding contribution to whole-canopy photosynthetic rates have not been quantified. An experiment using SPAR (Soil-Plant-Atmosphere-Research) chambers maintained at 16-h day/night thermoperiods of 14/10, 17/12, 20/15, 23/18, 28/23, and 34/29 degrees C was conducted. Mature canopies were divided into three horizontal layers of equal depth. Canopies were defoliated at each layer, from the ground upward, on successive days. Response curves for photosynthetic rate vs. irradiance were obtained after each defoliation. Leaf area within each layer followed a quadratic relationship with temperature. The largest areas were between 16.6 and 22.1 degrees C. Main-stem leaves accounted for > 50% of the total leaf area at temperatures < 22 degrees C, while the proportion of axillary-stem leaf area in each layer increased with temperature. Canopy maximum gross photosynthetic rates, A(MAX), before harvest ranged from 9.5 to 34.8 mu mol CO(2) m(-2) s(-1) (production-area basis) and were higher at 14/10, 17/12, and 20/15 degrees C temperatures than at 23/18, 28/23, and 34/29 degrees C. These values were largely related to the quantity of leaf area in each chamber. The value of AMAX and canopy light use efficiency declined as successive canopy layers were removed, primarily due to decreases in canopy light interception. These results indicate that the relative proportion of main- or axillary-stem leaves are not as important for potato canopy modeling considerations as is the need to simulate the correct quantity of leaf area.